This invention relates to a new molding composition which is particularly suitable for use in the manufacture of urns and decorative frames for mausoleum niches, picture frames and other durable articles of an ornamental or sculptural nature.
Modern mausoleums are constructed with hundreds of small niches or hollow cavities formed in their interior walls adapted to house urns containing cremated ashes of the dead, and framed by rectangular decorative frames mounted around the fronts thereof for holding glass so that the urns can be concurrently viewed while protected. Once installed, the frames and urns remain permanently in place. A metal, usually brass, is used extensively in making such frames and urns because they must be long-lasting, must have a decorative and durable appearance, must be made of a hard and strong material capable of being molded with intricate sculptural designs having sharp, clean surfaces and edges, and must not be susceptible to cracking or chipping over an extended period of time. However, rising costs and the shortage of brass or other suitable metals makes it very desirable that a more available material be found for such frames and urns, and for other ornamental articles such as picture frames, decorative borders, and the like which require similar strength, durability, moldability and appearance characteristics.
One possible group of substitute materials are plastics. However plastic materials, in their presently available form, are unsuitable for the foregoing applications because, while they can be exceptionally hard and strong, they have an easily detectable synthetic, nondurable appearance which is not desirable for use in mausoleums and other artistic applications where a long-lasting, substantial appearance is required.
Another possible substitute group of materials are earth products, particularly combinations of Portland cement, plaster of Paris (i.e. calcined gypsum and lime) and sand which, when mixed with water and allowed to set in a mold, form a hard casting having the shape of the mold. Combinations of such materials have previously been used for various purposes such as producing building blocks, artificial stone and dental investment. For example, Hansen U.S. Pat. No. 1,923,370 discloses the use of 5-95% calcined gypsum (CaSO.sub.4.sup.. 1/2H.sub.2 O) with 95-5% Portland cement to produce building blocks of various shapes which are particularly resistant to eroding action by water. Comins U.S. Pat. 218,490 discloses the use of equal parts of plaster of Paris, cement and sand, along with wood ashes and common salt, which may be used to produce artificial stone. Similarly, Gilbert U.S. Pat. No. 1,432,545 shows the use of one part dental plaster of Paris, three parts Portland cement and two parts silica (presumably silicon dioxide, the essential ingredient of sand). However, none of the aforementioned combinations of ingredients provides the combination of sufficient strength, durability, hardness, resistance to chipping and sculptural moldability qualities necessary for the production of the aforementioned types of ornamental articles.
Three factors which are of particular importance in governing the strength and sculptural qualities of an article molded from the aforementioned components are the type of plaster utilized, the amounts of plaster and cement relative to one another, and the amount of sand relative to the plaster and cement. It has been found that the use of mere plaster of Paris, that is, conventional coarse-ground calcined gypsum mixed with lime and setting retardation agents, results in a molded product of only moderate strength and unsatisfactory sculptural definition and sharpness. It has also been found that the strength of the product is reduced significantly and the setting time is increased significantly if an insufficient amount of calcined gypsum relative to Portland cement is used. In addition, the strength and sculptural quality of the product is seriously degraded if too much sand relative to the mixture of calcined gypsum and cement is used. Therefore, it can be seen that improvements in the character and relative quantities of the aforementioned components are needed if they are to be used in molding the aforementioned types of products which require high strength and durability, and exhibit good sculptural characteristics.